484 MEMOIRS OF THE CARNEGIE MUSEUM. 



supial structure, so that they may be males. Of the others, three are males, and 

 one is a gravid female with eggs. The fact that this was collected on July 20 gives 

 an indication of the breeding season. 



Anal opening (a in text-figure) closed above, without forming a supra-anal. 

 Closed part (s) two to three times as long as the anal; the latter (a) slit-like, short, 

 shorter than the branchial opening. Inner edge of anal practically smooth. 

 Anal separated from the branchial ])y a solid bridge (/) formed by the union of 

 the mantle-margins. Branchial opening (b) a little over twice as long as the anal, 

 with distinct papillae on inner edge; mantle-edges not united in front of it. Palpi 

 (h) subtriangular, the lower margins slightly convex, the posterior margins con- 

 nected at the base. 



Gills (/ and o) rather long and moderately wide. The inner (/) wider than 

 the outer (o) chiefly in front. Outer gill narrowing behind and before, its anterior 

 end near the highest point of the mantlc-attachment-line. The inner gill has an 

 almost straight lower margin, and is only little narrower anteriorly; its anterior 

 end is immediately behind the palpi. Inner lamina of inner gill entirely connected 

 with abdominal sac. 



Structure of gills normal. In the male both gills have fine, scattered, and 

 interrupted interlaminar connections, running parallel with the gill-filaments, 

 but without forming complete septa or water-tubes. In the gravid female, the 

 eggs are contained in the large middle section of the inner gill (/), leaving free 

 less than one-fourth of the gill at the anterior and at the posterior extremity, and 

 also leaving free a narrow zone along the margin. This marsupial part has the 

 interlaminar connections strongly developed, in the shape of interrupted septa, 

 forming incomplete, intercommunicating water-tubes, filled by the eggs in a dense 

 mass, not separated into placentae. Since no sterile females are at hand, the exact 

 arrangement of the interlaminar connections in a face view could not be made out. 

 The charged marsupium is somewhat swollen and distended, so that the inter- 

 laminar connections have stretched out. The outer gill of the female has the 

 structure of the gills of the male. 



2. Group of Diplodon granosus. 



Shell subovate or subtrapezoidal, rather elongated, not distinctly pointed 

 behind, straight, not distinctly higher in the posterior part, nor oblique. Beak- 

 sculpture well developed, but fine, and characteristically cut up into numerous 

 fine nodules or granulations, thus obscuring the radial arrangement. The granular 

 sculpture often continued a good distance upon the disk. 



